At the time of processing, such as cutting and boring, of a workpiece with use of a working machine, an unnecessary protrusion called “burr” may be generated on a processed surface of the workpiece. When the burr remains in the workpiece, the burr causes a defect of the product and an injury of the worker. Thus, a process of removing the burr (hereinbelow referred to as deburring) or a process of cutting a corner in which the burr is generated (hereinbelow referred to as chamfering) needs to be performed. Such a process is performed by a working machine for numerical control (NC) processes. To perform the process with use of the working machine, an NC program (also referred to as NC data) is required. By person in charge's inputting data directly into the working machine or by using shape data of the workpiece designed by computer aided design (CAD) software, a route of a tool attached to the working machine needs to be specified by computer aided manufacturing (CAM) software.
Meanwhile, in a case of boring a hole in a part of the workpiece, the burr generated in an opening rim on the backside needs to be removed. Since processing the workpiece by turning the workpiece upside down is poor in operability, a cutting tool enabling the backside of the workpiece to be processed is proposed (for example, refer to Patent Literature 1). In this tool disclosed in Patent Literature 1, a blade is configured to twist in a reverse direction of rotation, and deburring and chamfering in a secondary opening rim generated on a backside of a cylinder can be performed smoothly.